Last summer I wrote an article in Inspection Trends on Galvanization related Cracking of Structural Steel. The British Steel Construction Insitute is piblishing a guideline on this, might be out now.
Here is a link to the abstract for a paper about galvanized related cracking in a parking garage structure in Germany http://www3.interscience.wiley.com/cgi-bin/abstract/109568368/ABSTRACT Professor Gerhard Sedlacek discusses the tin and bismuth alloying in the galvanizing causing the problem.
Have an analysis done of the galvanizing look at tin, bismuth and lead levels.
Check the galvanizing thickness, the tin and other low melting point elements results in thinner galvanizing.
MT with AC, Yoke, red powder look for fuzzy indications.